U.S. Pat. No. 8,419,814 discloses depositing of a nano-sized titanium nitride, (TiN) and tantalum nitride (TaN) microstructures onto surfaces of cBN grains, by a process involving treating the cBN grains to make their surfaces vitreophillic, suspending them in ethanol, introducing Ta(OC2H5)5 and Ti(OC3H7)4, and further treating the suspension and cBN grains such that each cBN grain became coated with an intimate mixture of titanium and tantalum oxide compounds. The coated cBN grains were heat treated in suitable atmospheres to convert the oxides into nano-sized TiN and TaN. An aggregation comprising a plurality of cBN grains thus coated was formed and subjected to pressurisation at ultra-high pressure and high temperature, resulting in crack free PCBN material comprising about 84 volume percent cBN within a binder matrix substantially consisting of a mixture of TiN and TaN. In machining tests, the PCBN samples exhibited superior performance, which might have been due to the grain size of the binder matrix being close to the Hall-Petch nano-grain size.
U.S. Pat. No. 5,288,297 discloses a cBN compact comprising 40 to 90 volume percent of cBN crystals bonded by 60 to 10 volume percent of a bonding matrix comprised mainly of an intimate mixture of silicon nitride and metallic di-boride, where the metal is chosen from the group of titanium (Ti), zirconium (Zr) and hafnium (Hf) atoms. The silicon nitride and metallic di-boride each comprise at least 25 volume percent of the bonding matrix, which is strongly and coherently bonded to the cBN crystals. A method for producing the cBN compact by means of reaction bonding metal silicide compounds with the cBN grains is disclosed.
There is a need for relatively strong and wear resistant cBN composite material having relatively long working life when used to machine ferrous work-piece bodies, particularly but not exclusively in heavily interrupted machining modes.